[dbjorge]

Rolling your own CAPTCHA is very, very likely to introduce accessibility issues for your site. It is the accessibility equivalent of "rolling your own cryptography" for security. Among surveys of screen reader users, CAPTCHAs are regularly listed as the single most frustrating part of trying to use web sites via assistive technology.

Even if a CAPTCHA does offer a non visual alternative, it is very common for it to be inaccessible for folks with cognitive disabilities (eg, dyslexia) or motor impairments. Another common issue is assuming that users all speak English fluently. In this example, "beauty" is likely to be sufficiently culture specific to cause localization challenges.

https://www.w3.org/TR/turingtest/ is a good resource for learning about the accessibility implications of many common types of CAPTCHA implementation.